CFD modelling of black liquor recovery boiler NOx emission formation—Influence of envelope flame and thermal NO

IF 7.5 1区工程技术 Q2 ENERGY & FUELS

Fuel Pub Date : 2025-07-24 DOI:10.1016/j.fuel.2025.136309

Paulo S.P. da Silva, Markus Engblom, Leena Hupa

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引用次数: 0

Abstract

Fuel NO is considered the main source of pulp mill black liquor recovery boiler NOx emissions. The extent to which (i) NO chemistry when pyrolysis occurs with envelope flame as well as (ii) thermal-NO contribute to the boiler NOx emissions is currently unknown.

A CFD model of the recovery boiler was used to study these phenomena in recovery boilers. The CFD model includes fully coupled envelope flame prediction, with different source terms for volatile release with and without envelope flame. A simplified thermal NO expression was used to assess its formation. The recovery boiler modelled is a  600 MW 5300 tds/day boiler.

Accounting for the envelope flame did not result in significant changes in the temperature and O₂ profiles in the boiler. However, nitrogen chemistry was notably affected, with generally a decrease of 20 % in outlet NO when the envelope flame was considered. This decrease in outlet NO occurred due to the reduction of volatile nitrogen to N₂ in the envelope flame, as well as the re-burning chemistry, which reduced nitrogen species in the bulk gas. Various boiler cases with different levels of excess air as well as cases with different model assumptions concerning the split of fuel nitrogen into volatile and char nitrogen were analysed and the trends in outlet NO were similar whether or not the envelope flame was included. A similar trend was seen with different nitrogen splits.

When thermal NO was included in the model, an 18 % increase in outlet NO was observed. Thermal NO formation occurred close to the char bed in regions where the char bed carbon was being depleted.

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黑液回收锅炉NOx排放形成的CFD建模——包络火焰和热NO的影响

燃料NO被认为是纸浆厂黑液回收锅炉NOx排放的主要来源。目前尚不清楚(i)在包络火焰热解时NO化学反应以及（ii） thermal-NO对锅炉NOx排放的贡献程度。利用余热锅炉的CFD模型对余热锅炉中的这些现象进行了研究。CFD模型包括完全耦合的包络火焰预测，对有和无包络火焰的挥发性释放有不同的源项。采用简化的热NO表达来评估其形成。模拟的回收锅炉为 600 MW 5300 tds/天的锅炉。考虑到包络火焰并没有导致锅炉内温度和氧分布的显著变化。然而，氮化学受到明显影响，当考虑包络火焰时，出口NO一般下降20 %。出口NO的减少是由于包络火焰中挥发性氮还原为N2，以及再燃烧化学反应，减少了散装气体中的氮种。分析了具有不同过量空气水平的各种锅炉情况以及关于燃料氮分裂为挥发性氮和焦氮的不同模型假设的情况，无论是否包括包络火焰，出口NO的趋势都是相似的。不同的氮分裂也有类似的趋势。当模型中加入热NO时，观察到出口NO增加了18 %。热NO生成发生在靠近炭床的炭床碳被耗尽的区域。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Fuel 工程技术-工程：化工

CiteScore

12.80

自引率

20.30%

发文量

3506

审稿时长

64 days

期刊介绍： The exploration of energy sources remains a critical matter of study. For the past nine decades, fuel has consistently held the forefront in primary research efforts within the field of energy science. This area of investigation encompasses a wide range of subjects, with a particular emphasis on emerging concerns like environmental factors and pollution.